Process fob the manufacture of



Reiuued Feb. 16, 1943 UNITED STATES PATENT OFFICE PROCESS FOR THE MANUFACTURE OF ALUMINUM Hirsch Loevenstein, New York, N. YJassignor, by means assignments, of one-half to Independent Aluminum Corporation, New York, N. Y., a corporation of New York Original No. 2,198,678, dated April 30, 1940, Serial" No. 240,331, November 14, 1938.

Application for reissue April 28, 1942, Serial No. 440,870. In

France July 11, 1938 is claims.

The process at present in use for the manu- I facture of aluminum consists, on one hand, in the water and a great amount of labour: the manufacture of aluminum demands substances which are almost chemically pure, a great number of electric furnaces with a comparatively reduced individual capacity, and a great number of highly skilled workers. The manufacture of alumina is conditioned by the cost of the required coal, whilst that of aluminum is conditioned by the cost of the electric current; it is therefore often necessary to arrange the respective factories at a considerable distance from one another. On the other hand, the great amount of water implied in the manufacture of alumina, and the great number of electrolysing units in the manufacture of aluminum require a considerable surface in the layout of the plant, a high invested capital and large overhead charges.

A great deal of research work has been carried out with the view of developing a method for the manufacture of aluminum by a thermic process, 1. e. by a direct reduction of its oxide by carbon in a furnace at the suitable temperature. This research work has not given any interesting results, due to the fact that the aluminum, at the reduction temperature of the alumina, is already fairly volatile. Consequently, the aluminum vapours react with the carbon monoxide and with the carbon itself, thereby forming alumina and aluminum carbide. By this process, there is obtained, therefore, only a small amount of aluminum. the latter being, furthermore, soiled by the carbide.

Various pr have also been proposed for extracting the aluminum from certain of its alloys, as for instance the electrolytic refining of silico-aluminum, or the distillation of ferroaiuminum. All these attempts, however, have shattered either against technical difficulties or against the fact that the aluminum extracted in this manner ran up to an unreasonable price.

The object of the present invention is a process permitting to obtain aluminum from a certain number of its alloys as 'raw material, without presenting the drawbacks of the processes recalled above. a

For facilitating the comprehension of this process, one has represented on the annexed drawing a number of diflerent known curves.

Figure 1 is the curve of the system aluminumsilicon.

Figure 2 represents, at a larger scale, the left part of the curve of Figure 1, in order to show more clearly the solubility of silicon in the solid aluminum.

Figures 3 and 4 are curves showing the points of solidification of zinc and tin according to the proportion of aluminum.

The process consists in subjecting the raw material to the action of an alloy of a metallic treating substance, such as zinc, tin, mercury or various alloys of these metals, capable of forming with the aluminum an alloy which is comparatively rich in aluminum, which remains liquid at a temperature lower than the solidification point of aluminum and which, at said lower temperature, will not, to any considerable extent, 1. e. exceeding a few percent, form an alloy with the other constituents of the raw material, the above alloy being further easily separable from the aluminum, then separating the liquid alloy thus formed, from the solid residue at the said lower temperature, and lastly separating the aluminum from the alloyed treating metallic substance.

With this method, there is thus obtained, at a reduced cost, a comparatively very pure aluminum if this is desired, or an aluminum having various degrees of impurity sufficient for most of its uses.

The explanation of this result is the following:

The examination of for instance the curve of the system Al-Si (Figures 1 and 2) shows that there is a eutectic point lying towards the Al side,

at 13.8% Si. This means that if an alloy with for instance 40% Si be slowly cooled, there will occur, at about 1100*, a crystallisation of the silicon, while the remaining liquid will become richer in aluminum. At 575 C., the liquid aluminum willonly contain about 13% Si in solution. In this liquid are uniformly distributed in suspension the solid silicon crystals, the silicon being no longer dissolved. It is then possible, by the use of suitable means, to separate the solid part and obtain, in this manner, in the liquid state, an Al-Si alloy, which is less rich in silicon than the initial alloy.

By still further lowering the temperature, the whole mass will solidify at 575" while rejecting suddenly from the dissolved state, a high proportion of silicon. Beyond this temperature. only a small proportion of the silicon is left dissolved in the solid aluminum (1.65% at 575 0., as shown by the curve of Figure 2) the remainder is crystallised in the said solid aluminum. the substanceissolidthesaiddimolvedsiliconslowlygoesoverintothecrystallisedstateasflietemperature decreases. Iiitwerepouihleatalow temperature.toseparate fromthesolid aluminum all the crystallised silicon, this would provide the solution of theproblem of obtainingan aluminum withonlyalowpercentsge ofsilicon.i.e.the silicon contained in the form of a solid solution.

The same. or substantially the same consideratlonsmaybeappliedtothesystemsformedby aluminum withiron, or with titanium.

The problem faced by the inventor consisted therefore in providing a means permitting to obtain aluminum in the liquid state below its melt- (eutectic point oi Zn-Al). At this temperature. the aluminum only dissolves about 0.25% silicon (cf.1"igure 2) and practlcallynoiron at all. The extraction may therefore be commenced at 420 C. and ended at 380' C. One therefore descends on the melting curve of the system Zn-Al, on thesideoizmdowntotheeutectlc point, By adding cadmiumtothezinc,themelting temperature is correspondingly lowered (an alloy Zn-Cdwith20% Cdmeltsbelow380 0.): inthis way. of course. the dissolving power oi the bath for aluminum is decreased, since cadmium does 7 not dissolve aluminum, but at the same time the ingpoint. Thesolutiontothlsprobiemhasbem secured by the inventorbytreatlngthe above alloys by means of liquid metallic substances. which,intheliquidorvapmirstate,arecapable of dissolving a comparatively largeamoimt of aluminum'and a comparatively very small amount of its impurities, thereby forming alloys with a solidification temperature lower than the solidification point of aluminum (860') This is the case. for instance, for the above mentioned treatingsubstances,aslsshownbythecurves ofFigures3 and4,whichindicate the solidiiication pointsof zinc ortinbathsalloyedto variable proportions of aluminum.

The treating substance must further be easily separable from the aluminum which it dissolves, for instance either by distillation (this is the case to: zinc. mercury, zinc-cadmilmi alloys), or by electrolysis (inthecaseoi'tinhorfurtimrby metallurgical solutim (in the case of tneatment bytin.thetinbeingremovedbymeansofmolten lead).

Thepresenttreatmentoftheinitialmaterlals byametallicllquldorvaporoustreatingbodyis applicable particularly to the aluminum alloys obtalnedeitherbyreductiombymeansofcarbm intheelectrlciurnace,orbauxiteoranother aluminum ore containing, either theirmixtures;theprooessisalsopartlcularlyapplicabletothe treatmentofaluminumoralmninumalloyacrapsoroithesludgesiromthebatbs of molten aluminum.

Beiore being subjected to the,

amount of Fe and Si which dissolve in aluminum are advantageously reduced.

By adding cadmium, therefore (of. Example 2 below), theextracted aluminum is obtainedin a more pure state. but its cost price increases ,correspondingly, since its percentage in the extract ing metal decreases. The lower, thereiore. the extraction temperature, the pure: the obtained aluminum. V

Inthecasetinbechosenforthemetalofthe extracting liquid bath, the following should be remarked. The eutectic point Sn-Al (0!. curve ofEgure4,the1-ight'partofwhichhasbeen further represented at an enlarged scale) lies in close vicinity of theSn line. But at this temperature (229 0.), the tin dissolves only 0.5 aluminum. Themeltingcurveofthesystemrises hereveryrapidly. and at400 0., only 3.5% A1 aredissolvedinthetin. Byusingtimitwillbe more economical to use a higher extraction temperature. The extracted aluminum will be less pure,but since the elimination ottin will be eiiected electrolytically. giving a deposit of pure aluminum, the higher percentage of impurities intheextractedalummumisinthiscaseless important.

The inventor has found that the amounts oi impurities dissolved in the aluminum when the latter is itself dissolved in the treating bath at a temperature T: lower than the solidification point of almninum are precisely those existing in solid solution" in the solid aluminum at the said temperature TI. This means that matters mayheregardedasifthetreatingbath dissolves,

intherawmateriaLthesolidmaas'of aluminum eolelywiththosepartsofimpuiitieswhichare dissolvedintheaiuminuminastateofsolidsolution, plus the impurities soluble in the treatingbathitseli'.leavingasidethepart of impuritieswhiehisfreeinthecrystallisedstateintbe solidmassoi'aluminumandintherestoitheraw material; Tberesultisthat if,-after the solution oithesolid aluminum alloy'of theraw material inflietreatingbamthetemperatureoithisliquidmam isvaried, for instanoe'by lowering it from'li to 'lgtherewill'be depodted a quantity ofimpurlties correspcndingto the decrease, betweensald two temperatures,on'onehand of the coemcientofsoiidsolutionoi'theimpuritiesin thealummum,and,ontheotherhand of the cotherawmaterialhythetreatmentbathhadbeeneiiected directlyatthistemperature.

Thetemperatumoftheliquidmay therefore be brmht. after extraction at thetemperature Tntoiheiowesttemperature'la. corresponding toalowerpioportionotdissolvedimpuritieaand maytbenseparatefromtheliquldthepart of impurities which is rejected in the solid state inthe midst of tbeliquid mass.

The benefit of the present invention may also be obtained by performing the extraction at any suitable temperature, even superior to the melting point of the aluminum, if the temperature of the bath is thereafter decreased.

These various operating methods are of great importance. They enable the use of a liquid metal bath at a fairly high temperature, or even the vapours or such a bath, or both in succession. In order to carry out the present alloying treatment of the initial charge. e. g. of impure aluminum with a vaporous extracting metallic body the vapours of the latter are passed either through or over the solid initial product after the same has been broken up into comparatively small lumps. The vapours enter into contact with the impure aluminum of the initial material and an alloy is formed which is liquid even at a temperature which is much higher than the evaporation point of the extracting metal because the aluminum entering into the alloy with said metal greatly diminishes its vapour pressure. This alloy is separated in the liquid state; as it is formed at a comparatively high temperature the treating metal extracts from the initial material a relatively great amount of aluminum; it is true that on account of this elevated temperature the dissolution rate of the impurities in the extracted aluminum may also be relatively high; however, this is irrelevant because according to the essential principle of this invention it just sufilces to lower the temperature of the liquid alloy bath so that an essential portion of the dissolved impurities of which the solubility figure decreases with the temperature is precipitated and can be separated from the liquid bath. The treatment will be effected preferably by the counter-current method, i. e. the suitably broken up raw material and the treating liquid or vapour will be caused to travel in opposite directions respectively. There will thus be obtained an almost complete extraction or the aluminum from its alloys, and this in a short time if the operation is carried out at a high temperature, because the rapidity of the solution increases with the tempertaure. These various operating methods also permit to increase the aluminum percentage in the extraction bath and thus decrease its price. The curves of the solidification points of the alloys of the zinc or tin baths with aluminum in terms of the aluminum percentage (cf. curves 3 and 4) show that this solidification point rises with the proportion of aluminum. The result is that if the bath contains a greater proportion of aluminum, the temperature within which the bath remains liquid may be decreased less and consequently the aluminum will be obtained with a higher proportion of impurities: but, for certain applications, this higher proportion of impurities may be accepted or even desir These improvements furthe r permit to vary, within large limits, the extraction conditions, and thus substantially facilitate the technical and economical realisation of the process.

The liquid may be brought from the extraction temperature T1 to the desired temperature T: by suitable cooling and then maintaining it at rest at this temperature T: until the freed and solidifled amounts of impurities liquid. Such a decantation, considerable length of time.

It will often be advantageous to leave the liquid to solidify and then remelt it'at the temperature are separated irom the however, requires a '1': corresponding to the percentage oi aluminum contained; the quantities of impurities at this temperature will then remain in the solid state and will be immediately separable. Even if the melting and theseparation are effected rapidly the parts of impurities which may dissolve in the solid or liquid aluminum (it has been seen that the curves oi the solubility coeilicient were the same in both cases) when passing from the temperature of the soil mass to the melting temperature, will not have sufiicient time to dissolve entirely. By eilecting a number of successive meltings and taking advantage at each melting of the time lag in the solution of the impurities. the aluminum will be obtained more and more pure.

In the following examples, corresponding to tests carried out bythe inventor, the temperatures itgdticated are the temperatures at the end of the Example 1 20 g. or a silico-aluminum alloy obtained in the electric furnace and containing about 55% Al, 40% Si and 2.5% Fe were treated at ,a temperature 01' about 380 C., with 100 g. of Zn. The liquid part contained 5.37% Al, 0.023% Si and 0.0045% Fe. After eliminating the zinc by distillation, the aluminum obtained in this way contained 0.43% Si and 0.08% Fe.

Example 2 20 g. or an Al-Si alloy (of the same composition and origin as in Example 1) were treated, at a temperature below 380 C., with 100 g. oi an alloy containing Zn and 20% Cd. The resulting Zn-Cd-Al alloy contained 26% Al, 0.001696 Fe and 0.0043% Si. The aluminum thus extracted therefore contained 0.10% Si and 0.037% Fe.

Example 3 40 g. or an Al-Si alloy (the same as in Example 1) were treated at a dark red temperature, 1. e. at about 500, with g. of Sn. The obtained alloy contained 17.2% Al and 0.8% Si. Th extraction of aluminum from this alloy' may beobtained either by electrolysis or by treatment with liquid lead.

- Example 4' 12 g. of a silico-aluminum alloyisame as in Example 1) were treated at a temperature of about 800 C.- (very much above the eutectic point, 575, and even above the melting point of aluminum, 660) with 100 g. of Zn. The alloy thus obtained contained 1.062% Si, 0.020% Fe and 6.65% Al, corresponding to a percentage composition of 85.99% A1 with 13.75% Si and 0.26% Fe.

After cooling down and decantation at a temperature of about 390 C. (very much below the eutectic point Al-Si, 575") a metal dross containing the major part of the impurities floated on the surface and could thus be easily separated from the rest of the alloy. The alloy now contained 0.039% Si and 0.001% Fe, corresponding to a percentage composition of 99.43% Al and containing impurities to the amount of only 0.56% Si and 0.014% Fe. This result is very close to that of Example 1, where the solution was carried out at 380".

Example 5 12.13% 81 and 123% Fe. Alter remelting at 4 aggro.

'rhealloyobtainedwiththeextractionmeial contained use, s1, 021m 81 and 0.0082% re,

to a percentage composition of 07.33% Al. 2.07% Si and 0.005% Fe. Alter repeated melting (3 times) at a temperature oi about 400' 0., the alloy did not contain more than 0.0203! Bi and 0.0013% Fe. i. e. an aluminum with a percentage composition oi 00.63% Al, 0.30% Si and0.015% Pe.

Example 6 I 20 g. of a retro-aluminum with 00% Al, 35% Fe and about 3% 51 were treated at about 800 C.

with 100 g. oi Zn. The obtained alloy contained and 0.012'l% Si, correu 4.37% Al, 0.070% I' e sponding to a percentage composition or 08.24% A1 with 0.29% Si and 1.57% Fe. Alter remelting and decanting at a temperature of about 300' 0., the alloy did not contain more than 0.0055% 81 and 0.0092% Fe, corresponding to a percentage composition or 90.70% Al, with only 0.11% Si and 0.19% Fe as impurities.

Example 7 30 g. of an Al-Si-Fe alloy, the same as that of Example 5, were treated with 100 g. Zn at about in the liquid mm 050 C. The alloy thus formed contained 2.48% Si, 0.252% In: and 17.80% Al, corresponding to a percentage composition of 86.64% All with about 440 C. and decanting, the 81 percentage had gone down to 0.282 and the Fe percentage down to 0.019. The Zn was afterwards eliminated by distillatiom and the A1 remaining'in the i'umace had a'percentage composition of 98.37% A1, with 1.61% Si and 0.02% Fe as impurities.

More generally, it the extraction is eil'ected at a higher temperature, the aluminum obtained by this process contains higher amounts 0! iron or silicon, or both together. It is therefore possible, by varying the extraction temperature, to obtain aluminum alloys with a predetermined percentage of Si or Fe.

It is also possible to obtain aluminum alloys with the metals of the treating bath by limiting the elimination of the latter, for instance by stopping the distillation of the zinc or the zinccadmium, or by stopping the tin by means of lead. 50

solution of the It the two above operations are carried out in succession, alloys will be obtained containing at the same time the impurity metals of the raw material and those of the metallic treatingsubstance. 50

The process further permits to transiorm the mercially pure aluminum. It is also possible to extract by means or this process comparatively large amounts old aluminum or aluminum scraps into a comunder a reduced pressure or under vacuum with 5 or without the application of a reducing or an inert atmosphere.

The initial alloy remaining after extraction of the aluminum dissolved by the treating bath and which lsrich in iron or silicon or both, and 7 poor in aluminum, as well as the solid residue extracted from the treating bath, may be replaced into the electric furnace with the aluminum or with an ore suchas bauxite for serving again for the manufacture of aluminum alloys. 7

extracting the aluminum oi aluminum from the sludges no formed during the melting and remelting oi the the purified state from substances containing it in high proportions'together with at least one impurity oi the group consisting o! silicon. iron. titanium, comprising an alloying operation of the said'substance with at least a metallic extracting body oi the group consisting of zinc, tin, mercury and their alloys, and separating operation, at a temperature below the solidification point of aluminum, 0! the'liquld alloy and the solid bodies. a t

2. Process according to claim 1, in which the alloying action or the aluminum of the raw material with the metal treating substance is obtained by b ging into contact, in the countercurrent manner, the solid and suitably broken up raw material with the metal treating substance a '3.Processaccordingtoclaim1,lnwhichthe alloying action of the aluminum oi the raw material with'the metal treating substance is obtained by bringing into contact, in the countercurrent manner, the solid and suitably broken raw material with the metal treating substance 4. Process according to claim 1, in which the alloying action 01' the aluminum 0! the raw material with the metal treating substance is obtained by bringing into contact, in the countercurrent manner, the solid and suitably broken raw material with the metal treating substance in the vapour state.

5. Process according to claim 1, in which the alloying action of the aluminum of the raw material with the metal treating substance is obobtained by methodically b inging into contact, in the counter-current manner, the solid and suitably broken raw material with the metal treating substance first in the liquid state. and afterwards in the vapour state.

6. Process according to claim 1, consisting in from the substance containing it, by an alloying action with the metallic extracting body, at a temperature T1, then cooling the liquid alloy to a lower temperature T2, which is, below the solidification point of alumium, then eil'ecting at said lower temperature T1 the separation of the liquid bath and of the impurities released from the dissolved state and solidified by the cooling of the bath from Ti to T2.

7. Process according to claim 1, consisting in eil'ecting the extraction of the aluminum from the substance containing it, by an alloying action with the metallic extracting body, at a temperature T1, then cooling the liquid alloy to a lower temperature Ts, which is below the solidification point of aluminum, then eirecting by decantation at the said lowertemperature T: the separation or the liqupid bath and of the impurities released from the dissolved state and solidified by the cooling of the bath from T1 to T2.

8. Process according to claim 1, consisting in extracting the aluminum from the substance containing it, by an alloying action with the metallic extracting body, at atemperature T1, then cooling the'liquid alloy down to solidification, then remelting at a temperature '1: lower than the solidification point of aluminum and lower than T1, and separating the alloy which has become liquid from the solid impurities whichfat this lower temperature T2, have not gone in solution.

this lower temperature T: have not gone in solution, said remelting and separating at said lower temperature T: being effected a number of times in succession fairly rapidly in order that the amounts of impurities soluble at said lower temperature T2 are not given the time at each remelting to dissolve entirely.

10. Process according to claim 1,'comprising a reduction operation in the electric furnace of an aluminum ore in the presence of substances containing at least one of the metals of the group consisting of iron, silicon, titanium, an alloying operation of the impure aluminum with at least a metallic extracting body of the group consisting of zinc, tin, mercury and their alloys, a separating operation, at a temperature below the solidification point 01' aluminum, of the liquid body and the solid bodies, and the separation of the aluminum and the metallic extracting substance.

11. A process for producing aluminum comprising the steps of preparing a primary aluminum alloy from ore or ores containing aluminum together with at least one of the group consisting of silicon, iron and titanium, treating the said primary alloy with a metallic extracting agent of the group consisting of zinc, tin, mercury and their alloys to form an intermediate aluminum alloy with the'said extracting agent, separatin out the said intermediate alloy in liquid form from solid bodies of the said primary alloy at a temperature below the solidification point of aluminum, and breaking up the said intermediate alloy into its components.

12. A process for extracting aluminum from substances containing aluminum together with at least one 01' the group consisting of silicon, iron and titanium, comprising the steps of treating the said substance with a metallic extracting agent of the group consisting or zinc, tin, mercury and their alloys to form an intermediate aluminum alloy with the said extracting agent, separating out the said intermediate alloy in liquid iorm rrom solid bodies or the said substance at a temperature below the solidification point of aluminum, and breaking up the said intermediate alloy into its components.

13. A process for producing an alloy aluminum with at least one of the group consisting of silicon, iron and titanium, comprising the steps of preparing a primary aluminum alloy from ore or ores containing at least one of the group mentioned, treating the said primary alloy with a metallic extracting agent of the group consisting of zinc, tin, mercury and their alloys to form an intermediate aluminum alloy with the said extracting agent, separating out the said intermediate alloy in liquid form from solid bodies of the said primary alloy at a temperature below the solidification point oi aluminum, regulating the proportion of aluminum in the said intermediate alloy by controlling the said temperature of separation, and removing the said metallic extracting agent.

14. A process for producing an alloy of aluminum with at least one of the group consisting of silicon, iron and titanium from substances containing aluminum together with at least one of the said group, comprising the steps of treating the said substance with a metallic extracting agent of the group consisting of zinc, tin, mercury and their alloys to form an intermediate aluminum alloy'with the said extracting agent, separating out the said intermediate alloy in liquid form from solid bodies of the said substance at a temperature below the solidification point of aluminum, regulating the proportion of aluminum in the said intermediate alloy by controlling the said temperature of separation, and

removing the said metallic extracting agent.

15. A process for producing an alloy of aluminum with at least one of the group consisting of zinc, tin, and mercury, comprising the steps of preparing a primary aluminum alloy from ore or ores containing aluminum together with at least one of the group consisting of silicon, iron and titanium, treating the said primary alloy with a metallic extracting agent of the firstmentioned group to form an intermediate aluminum alloy with the said extracting agent, separating out the said intermediate alloy in liquid form from solid bodies of the said primary alloy at a temperature below the solidification point of aluminum, removing part of the said metallic extracting agent, and regulating the proportion of aluminum by controlling the extent of said extracting agent removal.

16. A process for producing an alloy 01' aluminum with at least one of the group consisting of zinc, tin and mercury from substances containing alumium together with at least one of the group consisting of silicon, iron and titanium comprising the steps of treating the said substance with one of the first mentioned group to form an intermediate aluminum alloy therewith, separating out the said intermediate alloy in liquid form from solid bodies of the said substance at a temperature below the solidification point of aluminum, removing part of the said metallic extracting agent, and regulating the proportion of aluminum by controlling the extent oi said extracting agent removal.

HIRSCH IDEVENSTEIN. 

